Question

15. a) How many groups and periods are there in Modern periodic table?
b) in the modern periodic table, how does the atomic size and valency change on
going
(I) left to right across a period?
(II) top to bottom in a group?​

Answer 1

Explanation:

a) there are 18 groups and 7 periods in a modern periodic table.

b)on going from left to right in a period the atomic size decreases.

on going from left to right in a period the valency first increases and then. decreases to 0

on going from top to bottom in a group the atomic size increases

on going from top to bottom in a group the valency remains the same